Re: OT: CO2 from a plane ride

On Mon, 23 Mar 2009 23:06:17 -0500, Jonathan Schattke
<wizwom@xxxxxxxxx> wrote:

Bill Snyder wrote:
On Mon, 23 Mar 2009 14:33:26 -0500, Jonathan Schattke
<wizwom@xxxxxxxxx> wrote:

Mike Ash wrote:
In article <gq593m$clq$1@xxxxxxxxxxxxxxxxxxx>,
Jonathan Schattke <wizwom@xxxxxxxxx> wrote:

Mike Ash wrote:
I find the idea horrifying because the power-to-weight ratio of nuclear
reactors is foolishly low, and so any nuke-powered airplane is going to
have ridiculously poor performance, and probably be poorly shielded too.
(Shielding is heavy!) And of course this feeds into your concern,
because aircraft with ridiculously poor performance are more prone to
accidents.
JPL has a 454kg 1 MW reactor. That 737,000 foot-pounds per second,
about 6 times what the GE90 used in the 777 produces. Now, Even
electrical motors aren't THAT inefficient.
Do you have a link to info about that reactor? It sounds very
interesting.
Regarding power to weigh ratios of nuclear reactors:
I was able to find this:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/7424/1/03-1279.pdf

Which has an existing design for a thermoelectric 2500kW reactor massing
4600 kg; That would give about 106,000 HP for the fuel mass. So, it's
power to weight ration is not quite high enough. Thermoelectric,
though, is very reliable, which is why it's chosen for space applications.

And because the electronics being powered are generally small, so
that radiation shielding for them doesn't mass or bulk a whole
lot. Now, if you need to shield the *generator* instead, because
the aircrew and groundcrew unaccountably object to glowing in the
dark . . .

And making a heat-generator bigger and bigger will get you a nice
fast education on the square-cube law.

Boiling water reactors are considerably more efficient than
thermo-electric - so even doubling the mass to have a power turbine, you
get 10x the power. So, ballpark, assume 9,000 kg for 25 MW; you're back
at the 400 MW area.

I think you really, really, *really* need to go check out the
actual size and mass of a reactor-based installation that's
capable of producing hundreds of MW of electrical power.

say, something like:
http://www.powergeneration.siemens.com/products-solutions-services/products-packages/steam-turbines/scale+smaller+150mw/pre-design/sst-predesigned.htm

A 10MW turbine/generator is 9m x 2.8m x 3.2m high; unfortunately,
Siemens doesn't tell me how heavy it is.

As far as it goes, I don't think anyone is currently working on an
aviation reactor.

That's only a start. If you're going to run a closed system, you
need to cool the steam afterward, and allow it to condense, and
pump the water back into the reservoir. On the ground, that's
normally done by a large water-water heat exchanger, using water
from a nearby river for the secondary cooling (because the
primary-loop water gets a bit radioactive). The secondary water
still gets (thermally) hot enough that you need a large assembly
called a cooling tower to cool it enough that you can put it back
into the river again.

If you're *not* going to run a closed system, you need to think
about how much water you plan to carry, and about whether you plan
to bribe the EPA and NRC guys, or shoot them, or what.

--
Bill Snyder [This space unintentionally left blank]
.

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